Skin is the largest organ, covering the entire human body, and has functions of preventing loss of body fluid, influx of toxic substances and microbes from the outside, and protecting the body from physical and chemical stimuli. In the case of a patient whose skin is seriously impaired by severe burns, injury, carcinoma excision, skin diseases and the like, a protective membrane is needed to prevent infection of impaired regions and the loss of body fluid, along with not leaving a scar at the impaired region and preventing serious shrinkage accompanied by the process of spontaneous cure. For regenerating impaired skin tissue, there are three methods of autograft in which a patient's own skin is transplanted, allograft in which the skin of another human being is transplanted and xenograft in which the skin of an animal is transplanted. Among them, autograft is the most ideal. However, when burnt areas are extensive, there is a limitation of the regions from which skin tissue may be obtained, and the harvesting regions can leave a new scar. Allograft plays a greater role in helping the movement of cells at the periphery of the impaired region and curing than permanent engraftment.
Specifically, in the case of a third-degree burn in which epidermis, dermis and subcutaneous layers are impaired, skin grafting is essentially required. At present, autograft is most often used as skin grafting. However, harvesting autograft tissue creates a new injury, increasing patient's pain, time for complete recovery can be extended, and the economic burden is greater. In addition, when insufficient healthy regions remain—as with a severely burned patient—autograft cannot be applied, or grafting operations should be performed repeatedly. To resolve the above problems, allograft using the skin of another person and xenograft using the skin of an animal such as a pig have been tried. However, other side effects as well as immunorejection often result.
In the case of burn surgeries which are most generally performed in domestic and foreign hospitals, the dead epidermis and dermis layers are removed and skin grafting is then carried out by using an acellular dermis in which the epidermis and cells in the dermis are removed from skin harvested from a corpse to avoid immunorejection. Cultured keratinocytes will then complete the entire skin thereon. Because such a completed skin includes basement membrane, it can play a role in protecting the body from external hazardous substances.
U.S. Pat. No. 5,336,616 discloses a method for preparing collagen-based tissues for transplantation. However, tissues prepared according to the method disclosed in the above patent have problems in that cryoprotectant ingredients do not sufficiently penetrate into collagen tissues, and low concentration of sugar cannot sufficiently exclude moisture from collagen tissues—which has a characteristic of absorbing lots of moisture—so that many ice crystals are formed at the time of freezing. Such ice crystals make many pores in tissues in the course of drying and destroy collagen tissues, and the tissues are rapidly degraded after transplantation so as not to maintain their structure and to be absorbed.